ROME -- When Amedeus of Savoy, who is duke of Aosta and a pretender to the throne of the Kingdom of Italy, started using the royal coat of arms to boost the export of his farm products, he rekindled an old family quarrel in Italy's royal house.

This latest in a series of differences between the duke and Crown Prince Victor Emmanuel of Savoy is a matter of dignity. The prince, main pretender to the throne, contends that it is vulgar to sell wine and less noble food products (such as sausages and pasta) bearing the royal coat of arms.

Victor Emmanuel's lawyer sent a letter to his cousin threatening legal action if the duke continued to insist on using the royal emblem for pecuniary purposes.

The duke, who is a "gentleman farmer," pointed out that the king of Greece sold wine marked with his family's arms and the Spanish Bourbon royal house of Orleans marketed a successful brandy under its name.

Besides, the duke argued, the names of Savoy and Aosta have been taken by numerous hotels and even an insurance company, a practice the royal family might try to use to obtain compensation from those without permission.

"So why should I not sell the produce of my own lands?" he asked.

While the duke explained, his administrator, Aldo Leonardini, sought to soothe those who looked askance at using the royal coat of arms to label less decorous products than wine or spaghetti or perhaps the odd sausage brand. "We would never put the coat of arms on tins of tomato extract," he said.

It was not the first time the two cousins, bitter enemies over the succession to a now meaningless throne, indulged in disputes over trademarks.

A few months ago the business-minded duke introduced his own brand of champagne called Savoy, prompting Victor Emmanuel to retort: "If he calls his champagne Savoy then I'll call my pigs Aosta."

Last month the duke explained that not all the produce sold with the royal coat of arms will originate from his own lands. Actually the bulk will come from an agrarian consortium the duke founded but whose products he promised to check personally for quality.

No love is lost between the two cousins, especially after Italy's biggest monarchist movement last February "dethroned" Victor Emmanuel as main pretender in favor of the duke. That royal gambit caused more amusement than concern among Italians, who abolished the monarchy in a 1946 plebiscite.

The monarchists accused the crown prince, who lives in exile in Switzerland, of a scandalous life- style, unbefitting a king.